Pressure switch



Oct. 22, 1968 H. R. CHAPIN PRESSURE SWITCH Filed Oct. 22, 1965 IIIII/ VII/l u m /I 8 8 .L s am 5 Z IO A. 2M u u a M u o2 .o A' 5 4 3 mvaNToR HOWARD R. Cwwm 3,407,277 PRESSURE SWITCH Howard R. Chapin, Park Ridgelll., assignor, 'by mesne assignments, to Controls vCompanyof America, Melrose Park, Ill., a corporation of Delaware Filed Oct. 22, 1965, Ser. No. 500,505 7 Claims. (Cl. 200,-83)

' ABSTRACT OF THE DISCLOSURE This disclosure relates `to a pressure switch ,wherein an overcenter snap switch is movable between a trip position and a reset position on the basis of a pressure condition which acts on a diaphragm and against a spring, the spring opposing diaphragm movement in response to increased pressure on the diaphragm. In accordance with this disclosure resilient lugs are arranged on the diaphragrn so as to engage the pressure switch housing to limit diaphragm movement in a reset direction. The lugs limit expansion'and relaxation of thevcalibrating spring to an amount insucient to relax the Calibrating spring to such an extent that it can shift its seat, but the resiliency of the lugshpermitsv them to accommodate overtravel.

This invention relates to pressure switches.

A typical pressure switch includes a snap switch (generally a toggle or overcenter switch), a diaphragm connected to the 4switch to exert an operating force on the switch in accordance with a particular pressure condition, and a compression Calibrating spring acting in opposition to the forcevexerted by the diaphragm. Such pressure switches are generally operable between trip and reset positions with the Calibrating spring being adjustable to determine the pressures as which trip and reset occur. In some instances pressure switches have been observed to lose their prescribed calibration in that, in operation they did not maintain the trip and reset actuating points established at initial calibration. It has been discovered that this loss of calibration was a result of the Calibrating spring,.on moving in a direction toward reset, being relaxed toA such a degreethat it shifted its seat. When its seat shifts the force exerted by the spring in opposition to thef diaphragm force is varied thereby disturbing the desired calibration of the pressure switch.

This invention is Concerned with .this lproblem of loss of calibration `and has a general object to provide a pressure switch construction which will hold a prescribed Calibration andthereby provide consistent operating characteristics. over extended operation and through the full range oftcalibrating spring adjustment.

For the achievement of this and ,other objects, this invention proposed an arrangement which limits the movement of the diaphragm inthe reset direction, and correspondingly the expansion and relaxation of the Calibrating spring, to an amount insufficient to relax the Calibrating spring tosuch an extent that it can shift its seat.

Other objects and advantages will be pointed out in, or beapparent from, the specification and claims, as will obvious'modications of the embodiment shown in the drawings, in which:

FIG. 1 is a section view of a pressure switch embodying this invention;

FIG. 2 is a partial sectioniview of the pressure switch illustrating operative engagement of the Calibrating spring relaxation limiting means;

FIG. 3 is a bottom view of the diaphragm; and

FIG. 4 is an enlarged view of the relaxation limiting means.

With particular reference to the drawing, pressure switch 10 includes an outer housing 12 of conventional 3,407,277 Patented Oct. 22, 19668 ICC construction. Diaphragm 14 is supported within the housing and divides the housing interior into pressure chamber 16 and switch chamber 18. Chamber 16 is adapted to be connected to source of pressure through conduit 19,. A double throw toggle type snap switch 20 is mounted in Chamber 18 and its operating tongue 22 is connected to diaphragm 14 through actuator post 24. Calibrating spring 26 is suitably connected to oppose diaphragm movement, for example having one end bearing on-or directly on the switch tongue as illustrated. The opposite end of spring 26 is seated in a movable adjusting capf128 to oppose the actuating force exerted on the switch by the pressure acting on the diaphragm. l

The force with which spring 26 opposes the force exerted by the diaphragm is adjustable by varying the position of cap 28. This adjustment can be accomplished in any suitable manner, for example through a conventional construction of screw 30 and adjusting cam 32. Screw 30 is threaded into cap 28 and cam 32 includes a plurality of lands 34, 36 and 38 separated by raised portions 40 and 42. Cam 32 is supported for rotation on shaft 44 and the radial distance between the shaft and the lands is dilferent so that the position of cap 28 in bore 46 can be varied by selective engagement ofscrew' 30 in one ofthe lands which correspondingly varies the compressive force exerted by spring 26 against the diaphragm force.

As illustrated in FIG. 2 the pressure switch is in a reset position. The diaphragm will bow upwardly as, the pressure in chamber 16 and on the undersideof the diaphragm increases. At a particular trip pressure, determined by the adjusted position of cap 28, switch 20 will go over Center moving movable contact 48 from reset Contact 52 to trip contact 50 with the pressure switch vassuming its trip position as shown in FIG: 1. As the pressure in chamber 16 decreases the diaphragm will move downwardly under the influence of spring 26 toward a reset position. At a particular pressure acting on the underside of the diaphragm the switch will reset. That is, at the reset pressure determined by spring 26 tongue 22 is moved overcenter and movable Contact 48 switches from trip Contact 50 to reset Contact 52.

In moving toward; the reset point the Calibrating spring is expanding and it has been discovered that this expansion of the spring can proceed to such an extent that relaxation of the spring is sufficient to permit the spring to shift its seat and thereby disturb the desired calibration set into the pressure switch. The pressure switch of this invention solves this problem by limiting movement of the diaphragm, and correspondingly expansion of the Calibrating spring, in the reset direction. This is achieved by providing limit stops between the underside of the diaphragm and housing 12. Specifically,

a plurality of lugs 54 are provided on the underside of the diaphragm and extend toward housing 12. The lugs 54 engage the housing in reset position, as illustrated in FIG. 2, and limit movement of the diaphragm such that the Calibrating spring cannot expand to a point Where the spring can shift its seat. Under normal operating conditions the -lugs hold the diaphragm so that spring 26 is at all times maintained under some degree of compression between Cap 28 and actuator post 24. Thus, the spring does not relax and it maintains the seating necessary to hold the desired calibration. In normal operation the lugs design is such that reset occurs before the lugs engage the housing so that the lugs do not interfere with reset operation.

The number of lugs can be varied as desired, for example satisfactory results have been obtained by using three lugs equi-angularly spaced around the operational center of the diaphragm (i.e. in line with actuator post 24).

well as automatic reset. In such applications arrangements such as that illustrated are used. More particularly, rotation of cam 32 to engage either rise 40 or 42 with screw moves cap 28` downwardly a sufficient distance to engage nger `56 with actuator post 24 and move switch tongue 22 overcenter to reset the switch. It will also be noted that as the cam islrotated to selectively engage one ofthe lands with screw 30 the switch is movedthrough reset by the actionv of rise or 42 on the screw and ca-p. To insure reset this movement is generally in excess of that which would be necessary to just engage lugs 54 with the housing. The force exerted on manual reset overcomes the support furnished by lugs 54 and 'to accommodate this additional movement, or overtravel, the lugs are generally made of resilient material so that they compress and do not interfere with manual reset movement and, moreover, so that they automatically return the diaphragm and actuator post to the desired position afterrelease of the manual reset force to thereby prevent relaxing and shifting of the spring. Movement past the lower limit determined by the lugs is not detrimental in manual reset because the cap 28 is being moved downwardly and the spring is maintained in compression during this reset movement. Preferably lugs 54 are molded as an integral part of the diaphragm and are hollow as illustrated in FIG. 3 which contributes to their being capable of accommodating overtravel.

Although but one embodiment of the present invention has been illustrated and described, lit will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

I claim:

1. A pressure responsive control comprising, in combination,

a housing,

control means in said housing and movable between rst and second operative positions,

a diaphragm in said housing and connected to said con trol means and operative in response to a change in a pressure condition on said diaphragm to move said control means toward said first operative position,

spring means lconnected to said control means and exerting a force on said control means in opposition to the force exerted through said diaphragm and in a direction toward said second operative position,

Iand-motion limiting means in said housing and arranged to limit movement of said diaphragm in the direction toward said second operative position when said control means has assumed said second operative position so that spring force is maintained between said spring means and said diaphragm in said second position and said spring means maintains a preselected calibration, said motion limiting means further characterized by being resilient and co1- lapsible, and in response to a force applied to said diaphragm in excess of said spring means force will yield to accommodate overtravel of said diaphragm in the direction .of movement toward said second operative position, and will automatically return the diaphragm to desired position after release of said excess force.

2. The pressure responsive control of claim 1 includving means supporting said spring means to exert a compressive force on said control means in opposition to said diaphragm force,- -5 and wherein said motion limiting means limits said dia- BERNARD A. GILHEANY, Primary Exzjitiiigr., f'

4 phragm and spring means lmotion to maintain said spring means under compression at all times. 3. A pressure switch comprising, in combination, a housing, switch means in saidhousing kmovable between trip andzreset positionsff f; j. w a diaphragm in said .housing-andconnected to said switch means to move saidnswitchmeans .toward said trip position in response 'to achangein a pressure conditionon'said diaphragm,x spring means connected to said switch means and seated to exert a force on 'said' switch means in opposition to-the force exertedfthrough saidfdiaphragm and in a direction toward said reset position, said diaphragm having a surface'facing towar'dhawall of said housing, said surface moving away from said housing wall as said switch meansris moved toward its trip position and toward said housing wall as said switch means is moved toward its reset position, and motion limiting means in the form 'of hollow resilient Ilugs -arrangedintermediate said diaphragm surface and said housing wall and operative to'lirnit movement of said diaphragm in a direction toward said housing wall when said switch means has assumed said4 reset position so that spring" force is maintained between said spring means and said diaphragm in saidreset position and said spring means maintains a preselected calibration, said lugs being resilient and collapsible, and in response to a force applied to said diaphragm in excess of said spring means force will yield to'accommodate overtravel of the diaphragm inthe direction of movement toward said reset position, and will automatically return said diaphragm to desired position after release of said excess force. l i' 4. The pressure switch of claim 3` including adjusting means connected to said 'springmeans and operative to adjust said spring means to vary' the force exerted thereby in opposition to the force exerted through said diaphragm, vvand means connected to said switch means andv selectively operable to movesaid switch-means to said f reset* position substantially independent of thepressure on said diaphragm. 5. The pressure switch of claim 3 wherein said lugs are connected to and movable with said diaphragm toward and away from said housing wall and engage said housing wall when said switch means reaches said reset position. Y

6, The pressure switch of claim 5 wherein said hollow lugs are integral with said diaphragm. l

7. The pressure switch of claim 6 wherein said spring means is supported to exert a compressive force onfsaid switch means and said lugslimit relaxation of said spring means to maintain said spring means in compression and securely seated at all times. v

- v ReferencesCited UNITED sTATEs PATENTS 

